It is known from Letsinger et al, Nucleic Acids Research 1975, vol. 2, pages 773-786, that oligonucleotides may be chemically synthesised by the sequential addition of suitably elaborated nucleoside derivatives to a shorter oligonucleotide which is covalently linked to a solid polystyrene support. Other types of solid support have also been used for this purpose, for example, cellulose, as described by Crea and Horn, Nucleic Acids Research 1980, vol. 8, pages 2331-2348, polyacrylamide, as described by Gait et al, Nucleic Acids Research, 1982, vol. 10, pages 6243-6254, silica, as described by Caruthers et al, Tetrahedron Letters, 1980, vol. 21, pages 719-722, and controlled-pore glass, as described by Sproat et al, Tetrahedron Letters, 1983, vol. 24, pages 5771-5774. In these known methods, the simultaneous synthesis of several different oligonucleotides can be accomplished only by performing each synthesis independently, thus demanding considerable investment in equipment and operator time.
Simultaneous synthesis of several different oligonucleotides has been described by Frank et al, Nucleic Acids Research, 1983, vol. 11, pages 4365-4377, using cellulose discs as the solid support. However, this method is very laborious in that each individual disc must be dried and sorted at the conclusion of each stage of the synthesis, and thereafter transferred to the appropriate reaction vessel prior to the next stage. This complex procedure enhances the probability of failure of a synthesis caused by moisture absorption during handling, or by operator error during the sorting process. In addition, the quantity of each oligonucleotide that may be prepared in any single synthesis is limited by the capacity of the cellulose disc used. Furthermore, the method is only capable of applicatin to synthetic methods employing solid support materials which can readily be formed into coherent, mechanically stable discs.